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| United States Patent |
5,575,928
|
|
Peltier, Jr.
, et al.
|
November 19, 1996
|
Process and product produced thereby for disinfection and agricultural
reuse of organic sludges
Abstract
There is disclosed a process and product made by said process, for
conversion of organic waste sludges bearing potentially pathogenic
bacteria into a non-odoriferous, non-pathogenic agricultural medium which
is highly nutritious to plant life; which process includes: blending the
organic sludge with an effective amount of at least one of a class of
chemical compounds which form methyl isothiocyanate ("MITC") in aqueous
solution, such as sodium N-methyldithiocarbamate; blending the MITC
treated sludge with an effective amount of electrolytic soil additive;
blending the MITC and soil conditioner treated sludge with an effective
amount of a hydrophilic polymer, such as potassium polyacrylate; and,
blending the MITC, soil electrolytic additive, hydrophilic polymer treated
sludge with organic bulking agents and inorganic conditioning materials.
| Inventors:
|
Peltier, Jr.; Morris (1140 Honeycomb Dr., Cade, LA 70519);
Mayeux, Jr.; Eddie P. (125 Walker Gravel Pit Rd., Dry Prong, LA 71423)
|
| Appl. No.:
|
341801 |
| Filed:
|
November 18, 1994 |
| Current U.S. Class: |
210/764; 422/28; 422/32 |
| Intern'l Class: |
C02F 001/50; C02F 011/00 |
| Field of Search: |
210/764
422/28,32
71/11,12,13,14,23,24,25
|
References Cited
U.S. Patent Documents
| 3942970 | Mar., 1976 | O'Donnell | 71/12.
|
| 4067896 | Jan., 1978 | Pierce | 424/302.
|
| 4729831 | Mar., 1988 | Fujino | 210/631.
|
| 4732684 | Mar., 1988 | Fujino | 210/631.
|
| 4935447 | Jun., 1990 | Philips et al. | 514/640.
|
| 5077314 | Dec., 1991 | Philips et al. | 514/640.
|
Primary Examiner: McCarthy; Neil
Attorney, Agent or Firm: Onebane, Bernard, Torian, Diaz, McNamara & Abell Law Firm
Claims
What is claimed is:
1. A process for exterminating pathogenic bacteria in organic waste sludge
comprising the step of thoroughly mixing said organic waste sludge with an
effective amount of an aqueous based solution having a solute of at least
one of a group of chemical salts, which said salt spontaneously releases
gaseous methyl isothiocyanate when said salt is dissolved in an aqueous
based solution.
2. The method of claim 1 wherein the group of chemical salts which
spontaneously release gaseous methyl isothiocyanate when said chemical
compound is dissolved in an aqueous based solution comprises at least one
of a group of monomethyldithiocarbamate salts of any cation.
3. The method of claim 2 wherein the monomethyldithiocarbamate salt used
comprises at least one having a metal cation.
4. The method of claim 3 wherein the monomethyldithiocarbamate salt used
comprises at least one of a group of salts having sodium as a cation.
5. The method of claim 4 wherein the monomethyldithiocarbamate salt having
a sodium cation comprises sodium N-methyldithiocarbamate.
6. The method of claim 3 wherein the monomethyldithiocarbamate salt used
comprises at least one having a potassium cation.
7. The method of claim 6 wherein the monomethyldithiocarbamate salt having
a potassium cation comprises potassium N-methyldithiocarbamate.
8. The method of claim 1 wherein the group of chemical salts which
spontaneously release gaseous methyl isothiocyanate in gaseous form when
said chemical compound is dissolved in an aqueous based solution comprises
at least one of a group of monoalkyldithiocarbamate salts of any cation.
9. The method of claim 1 wherein the amount of chemical salts which
spontaneously release gaseous methyl isothiocyanate in gaseous form when
said chemical compound is dissolved in an aqueous based solution is at
least 8 fluid ounces per ton of organic sludge.
10. The method of claim 1 further comprising the step of thoroughly mixing
an effective amount of water based, biodegradable, electrolytic soil
additive with the organic sludge.
11. The method of claim 1 further comprising the step of thoroughly mixing
an effective amount of hydrophilic polymer with the organic sludge.
12. The process of claim 1 further comprising the step of thoroughly mixing
an effective amount of at least one of a group of non-pathogenic, organic
bulking material.
13. The process of claim 1 further comprising the step of thoroughly mixing
an effective amount of at least one of a group of non-pathogenic,
non-organic soil conditioning agents.
14. The process of claim 10 further comprising the step of thoroughly
mixing an effective amount of hydrophilic polymer with the organic sludge.
15. The process of claim 10 further comprising the step of thoroughly
mixing an effective amount of at least one of a group of non-pathogenic,
organic bulking material.
16. The process of claim 10 further comprising the step of thoroughly
mixing an effective amount of at least one of a group of non-pathogenic,
non-organic soil conditioning agents.
17. The process of claim 14 further comprising the step of thoroughly
mixing an effective amount of at least one of a group of non-pathogenic,
organic bulking material.
18. The process of claim 14 further comprising the step of thoroughly
mixing an effective amount of at least one of a group of non-pathogenic,
non-organic soil conditioning agents.
19. The process of claim 17 further comprising the step of thoroughly
mixing an effective amount of at least one of a group of non-pathogenic,
non-organic soil conditioning agents.
20. The method of claim 10 wherein the effective amount of water based,
biodegradable, electrolytic soil additive is approximately 4 to 12 fluid
ounces per ton of organic sludge.
21. The process of claim 11 or 14 wherein the effective amount of
hydrophilic polymer is approximately 1-3 pounds per ton of organic sludge.
22. The method of claim 12, 15 or 17 wherein the effective amount of
non-pathogenic, organic bulking material is approximately 1 to 3 times the
volume of the organic sludge.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention disclosed herein relates generally to the field of treating
organic waste sludges to reduce and/or remove viable pathogens and/or
vector attraction, so that such sludges may be safely and beneficially
reused. More particularly the invention disclosed herein relates to
conversion of said sludges, which are inherently highly nutritious to
plants, into a safe, enriched agricultural medium. With more particularity
the invention relates to conversion of the sludge into a form that is
convenient to use, and is conditioned to improve the ability of plants to
extract nutrients from the rich organic materials included therein.
2. Description of Prior Art
Organic waste sludges presently constitute a substantial problem in many
areas of the world. Such wastes are by-products of municipal and private
waste treatment plants, feed lot operations, sawmills, paper mills and
many other industrial operations.
A problem with such organic sludges is that they provide an excellent
growth medium for many types of potentially pathogenic bacteria, which are
almost inevitably introduced into said sludges by the influent waste.
Accordingly, raw organic sludges can be dangerous to human, animal and
plant life, and proper disposal or reuse of them constitutes a substantial
problem.
Said sludges are also typically odoriferous, have substantial vector
(pests, such as rats, mice, roaches and some birds) attraction, and exist
in the form of a sticky, wet, cohesive mass. These characteristics
substantially limit where such sludges may be acceptably disposed, make
dispersion difficult and entail the risk of vectors widely dispersing any
pathogens remaining in the sludge.
However, the nutritious properties of organic sludge which cause
potentially pathogenic organisms to flourish, also provide a potentially
highly beneficial use for said sludge, as an agricultural enriching
medium, provided that the potentially pathogenic organisms, vector
attraction and difficult handling characteristics can be significantly
improved.
A number of methods, described in 40 CFR Part 257, are known to reduce
pathogens. These include aerobic digestion, anaerobic digestion, lime
stabilization, air drying, composting, heat drying, heat treatment, gamma
irradiation, electron irradiation and the methods shown on Table 6-1 of
said regulation. In addition thereto U.S. Pat. Nos. 5,281,341 and
4,793,927 to Reimer's disclosed methods for treating waste sludge with
nitrous acid or ammonia. All of the previously known methods involve one
or more of the following disadvantages:
a) substantial time of treatment,
b) high energy usage,
c) substantial use of complex and expensive equipment, and,
d) transport of pathogen bearing sludges to a permanently located treating
facility.
The invention disclosed herein substantially reduces these disadvantages by
providing a fast, simple, inexpensive method of treating organic wastes,
on site, with simple, portable equipment. The invention further teaches
recycling of the treated sludge into an agricultural medium of highly
beneficial characteristics.
3. Objects of the Invention
The principal object of the invention is to provide a process by which
organic waste sludges can be quickly and cheaply treated to remove and/or
reduce potentially pathogenic bacteria, and eliminate or reduce vector
attraction. Another object of the invention is to provide a highly
beneficial product and process for making said product, which effectively
makes said treated sludge recyclable as an agricultural medium and/or soil
enriching/conditioning agent.
4. Description of the Preferred Embodiment
The preferred embodiment of the invention includes a first step of
disinfecting an organic waste sludge possibly harboring pathogenic
bacteria, then processing the disinfected sludge in a series of steps
designed to improve both the handling characteristics of the end product
and the ability of plants to extract nutrients from the end product,
thereby creating an end product highly suitable for use as an agricultural
medium and/or soil enriching/conditioning agent.
In the disinfecting step of the process the organic sludge is thoroughly
mixed with an aqueous solution of a salt that will produce methyl
isothiocyanate ("MITC"). One such salt, sodium N-methyldithiocarbamate
("SNMDC"), commonly used as a soil fumigant for control of weeds,
parasitic nematodes, and fungi, is both economical and effective. Other
alkali metal salts of monoakyldethiocarbamate salts of any cation, such as
sodium, potassium, lithium, or cesium, or heavier metals may also be used
but may be more expensive to manufacture. Alkaline earth metal salts, such
as magnesium, calcium, strontium, etc., of monomethyldithiocarbamate or
monoakyldethiocarbamate could also be used. Regardless of which salt of
monomethyldithiocarbamate or monoakyldethiocarbamate is employed, the
active biocide generated is MITC. MITC reacts with primary or secondary
amine groups on biologically important molecules, such as enzymes, to form
thioureas, thereby altering said molecules so that they can no longer
perform their biochemical function. Since MITC reacts with a wide variety
of biomolecules, it forms an effective biocide for known pathogenic
bacteria found in organic waste sludge.
While dosage may vary according to the MITC releasing agent used,
temperature, moisture content and bacterial contamination of the sludge,
we have found that a thorough mixing of 8 fluid ounces of SNMDC per ton of
sludge was effective in exterminating known bacterial pathogens in a
sample of municipal waste sludge. In addition to disinfecting said sludges
of pathogenic bacteria, the aforesaid step substantially reduces the
odoriferous characteristics and vector attraction of said sludge.
After disinfection as aforesaid, the sludge may be treated with a water
based, biodegradable, electrolytic soil additive, such as "Agri-SC Soil
Treatment" by Four Star Services, Inc. into the admixture, at the rate of
4-12 liquid ounces per ton of sludge. Such additive has two beneficial
effects. First, its wetting properties insure penetration of water,
bearing MITC, in and between the particulate matter of the sludge, thereby
increasing the probability of contact with all pathogenic bacteria that
may be harboring therein, thereby increasing the probability of complete
disinfection. Secondly, inclusion of such electrolytic additive in the end
product results in an improved agricultural product breaking hydrocopic
rings which exist around colloidals included therein, improving the
ability of plants to extract nutrients therefrom.
The third step is adding hydrophilic polymer, such as potassium
polyacrylate, may be introduced into the disinfected admixture. Said
polymer absorbs excess water from the sludge, effectively "drying" same,
so as to make it less cohesive and easier to handle. The addition of
polymer also improves the water retention characteristic of the admixture,
which produces a number of desirable effects. First, improved water
retention characteristics reduce the ability of odoriferous molecules to
escape from mixture, further reducing odor and vector attraction.
Secondly, increased water absorption provides for increased retention time
of MITC dissolved therein, thereby providing an increased period of
contact between MITC and pathogenic bacteria. Finally, increased water
retention, and reduced evaporation, improve the characteristics of the end
product as an agricultural medium and/or soil conditioning agent. Mixing
of approximately 2 pounds of powdered potassium polyacrylate per ton has
been found effective for sludges bearing approximately 80% water content.
Dosage may, however, be varied depending on the absorbency of the
particular hydrophilic polymer chosen. Any amount of hydrophilic polymer
may be added to produce a desired amount of "drying" of the sludge, and
desired water retention characteristics of the end product.
A final, also optional, step in making an easily usable agricultural
medium, is the inclusion of bulk, non-pathogenic organic and/or
non-organic conditioning material. An almost endless variety of such
materials may be used, to bind the highly enriched organic sludge to
particulate matter which tends to remain in place, and to impart desired
soil conditioning characteristics to the end product. Common additions may
include seed husks, hulls, shells, sawdust, ground animal shell and bones,
boiler ash, crop stubble, leaves, hay, grass, charcoal, carbon black,
diatomaceous earth and other organic matter. Conditioning agents such as
sand, mica, vermiculite, limestone and the like may also be used,
according to the conditioning properties desired in the end product. Once
these materials are blended with the sludge, (especially sewer sludge) the
cohesive texture of the sludge is further reduced and the end product has
the consistency of a potting soil type texture. This makes it much easier
to apply to or in the soil with the existing, simple, conventional
application equipment of the agricultural industry.
In one test approximately 1400 lbs of sludge was treated and thoroughly
mixed with approximately 2800 lbs of sawdust. The end product was a dark,
finely divided, non-cohesive, powder having a slight smell of freshly
tilled earth, which was found free of pathogenic bacteria.
Further testing of said process is undergoing for extermination of helminth
ova and enteric viruses, and though no claim is yet made respecting these
potential pathogens, the process is expected to substantially reduce, if
not eliminate both as viable pathogens. If not, a step of treatment with
ammonia, also known to be beneficial to plants, may be included in the
process.
The above-described preferred embodiment should be interpreted as
illustrative and not in any sense of limiting the scope of the invention,
which is set forth by the following claims and their equivalents.
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